Vitamin D-dependent recruitment of DNA-PK to the chromatinized negative vitamin D response element in the PTHrP gene is required for gene repression by vitamin D.

Abstract The mechanism of transcriptional repression by nuclear hormone receptors, especially in the presence of the ligands, is largely unknown. We previously reported that 1,25-dihydroxyvitamin D 3 (1,25 vitaminD 3 ) inhibited expression of the parathyroid hormone-related polypeptide (PTHrP) gene through the interaction between the liganded monomeric vitamin D receptor (VDR) and the negative DNA element in the PTHrP gene (nVDRE RP ). In this study, we employed chromatin immunoprecipitation (ChIP) assay and confirmed that 1,25 vitaminD 3 recruited DNA-dependent protein kinase (DNA-PKcs) to the chromatinized nVDRE RP . Conversely, the regulatory subunits of DNA-PK were associated with the nVDRE RP sequences only when 1,25 vitaminD 3 was absent. VDR was constitutively associated with these chromatinized nVDRE RP sequences. Furthermore, DNA-PKcs could phosphorylate VDR in vitro. We raise a possibility that a conformational change of VDR through its phosphorylation mediated by DNA-PKcs underlies the mechanism of gene repression by 1,25 vitaminD 3 -bound VDR.